Transcranial magnetic stimulation
Transcranial magnetic stimulation (TMS) has been exploited to advance knowledge of corticospinal physiology and, in a number of conditions, to aid diagnosis and quantify corticospinal abnormalities. The basic physics of magnetic stimulation is described along with the effects of stimulating coils with different dimensions and shape. The effects of single TMS pulses over motor cortex to cause a descending volley of D and I waves, and their effects on spinal motor neurons resulting in a motor evoked potential (MEP) are described. Guidelines for the safe use of TMS are given. Methods to estimate useful clinical measures of corticospinal function, such as threshold, MEP amplitude, central motor conduction time, silent period and input:output relation are given, as is the means to quantify corticospinal conduction using the triple stimulation technique. The clinical utility of TMS in neurodegenerations, central demyelinating diseases, stroke, spinal cord disease, movement disorders, and functional disorders is discussed.